The invention relates to a bypass turbojet engine airplane propulsion system comprising a nacelle borne by an intermediate case of the engine and which delimits a space for the flow of bypass air around the turbojet, this bypass air being intended to provide more than 80% of the thrust.
The engine is generally secured under a wing or to part of the fuselage or of the empennage of the airplane, by means of a pylon which is a part that is very robust and very heavy and is attached to the engine at several points through suspensions through which the loads transmitted between the engine and the airplane pass.
The fact that the engine is attached using a pylon and suspensions also means that the thrust is reacted along a line that is offset from the axis of the engine, leading to overall flexing in the engine case line. The pylon is also attached to the engine by elements which cross and partially obstruct the stream through which the bypass air flows through the nacelle, meaning that the radial dimensions of the nacelle have to be increased accordingly even though airplane manufacturers would rather wish to reduce these dimensions, particularly in the case of engines with high bypass ratios.